Known optical devices utilize diffraction gratings or beam splitters to couple collimated light out of a waveguide and into the eye of a user. The basic physics of these structures result in light being inefficiently coupled out of the waveguide from the consideration of the eyebox geometry. The beam splitters (essentially using reflection of the internal waveguide rays to out couple them) or diffraction gratings (using the corresponding phase of the internal waveguide plane waves to obtain transmitted/reflected diffraction orders) share the property that the out coupled collimated light is diverging with respect to the eyebox.
In standard waveguide helmet mounted display (HMD) technologies one of two ways of filling the eyebox is generally utilized. First, the original pupil may be largely oversized so that the eyebox can be filled with a small fraction of the image (and the rest lost). This results in relatively large collimators and waveguide substrates. A second way to fill the eyebox is to use a pupil replication technique, where an initial small pupil is input into the waveguide. As the pupil propagates down the waveguide it interacts with intermediate structures such as diffraction gratings or beam splitters that produce one or more copies of the original pupil travelling in a different direction to the original pupil. Pupil replication may be used to create a large pupil in both fields of view. The subsequent penalties resulting from pupil replication include a non-uniformity across the field and a banding of the replicated pupils as a function of the field. These limitations are inherent in pupil replicating designs. Therefore, there is a need to overcome one or more of the abovementioned shortcomings.